1. Field of the Invention
The invention contains a process for the determination and correction of laser induced damages of the optical and electronic components within the beam path of a monitor module of a 193 nm or 157 nm excimer lasers.
2. Description of the Related Art
Excimer lasers emitting pulsed UV-radiation are becoming increasingly important instruments in specialized material processing. The KrF-excimer laser emitting around 248 nm and the ArF-excimer laser emitting around 193 nm are currently the light sources of choice for photolithographic processing of integrated circuit devices (IC's). The F2-laser is also being developed for such usage and emits light around 157 nm.
It is recognized herein that it is desired in the field of industrial silicon processing that each of the above laser systems become capable of emitting a narrow spectral band around a very precisely determined and finely adjustable wavelength. It is further recognized that it is desired to have techniques for reducing bandwidths by special resonator designs to less than 100 pm for semi-narrow band lasers, to less than 1 pm for narrow band lasers, and to less than 0.6 pm for very narrow band lasers. It is further recognized that it is desired to have techniques for tuning and controlling central wavelengths of emission.
The wavelength of the emitted laser radiation can be determined by an etalon spectrometer. The etalon spectrometer produces interference fringes which are projected onto a CCD line. From the interference fringes the wavelength can be calculated.
From experimental results it is known that optical components and measurement equipment like CCD lines can be damaged by the UV radiation of an excimer or molecular fluorine laser. This causes problems especially for the measurement equipment, because reliable performance information is necessary for the lithography production process.
CCD cameras which are presently used can show degradation under UV radiation. The present invention avoids the described difficulties by using a special correction of the sensitivity of each camera pixel.